If you want to test against a demo environment, you can get a free Developer instance at http://developer.force.com. Developer instances work like production instances (but have pretty tight user and data limits), but would thus be accessible by this plug-in.

That said, it's pretty tough to corrupt a Salesforce database. I mean, you can pour a lot of dirty data in there with forms and this add-on, and that could affect your reporting, and all that comes with poor data integrity, but you're not going to "break" Salesforce by creating new records with forms and this add-on. As long as you're not writing into record ID fields, you shouldn't write over existing data either, just create new records.